1. Field of the Invention
This invention relates to an improvement of a pneumatic radial tire provided with a belt including a folded layer of metal cords.
2. Description of the Prior Art
In the belt of the radial tire are preferably used metal cords, particularly steel cords as an inextensible reinforcing material. For the structure of the belt, there is known a structure wherein plural layers each containing cords inclined at a small angle of 5.degree.-25.degree. with respect to an equatorial plane of the tire are simply placed one upon another so as to cross the cords of one layer with the cords of the other layer. A so-called fold belt is also known wherein both end portions of one of plural layers constituting the belt are folded in its withwise direction and such folded layer is placed on the other non-folded layers in various forms, and the like.
The fold belt is excellent in the cornering stability and advantageous in the high-speed durability because the circumferential rigidity is high owing to the folding effect of the cord layer as compared with the structure of simply placing cord layers one upon another. In the fold belt, however, the inclination angle of the cord with respect to the equatorial plane of the tire is small, so that the cords located at the folded portion of the cord layer is locally subjected to excessive tension, whereby the cord breaking is apt to be caused under an influence of not only an external force during the running but also an internal pressure applied in the vulcanization building of the tire. As a result, the improvement of expected durability is not yet developed at present.